Mountain bikes have overtaken road bikes in popularity over the past few years, with sales of mountain bikes exceeding those of road bikes by at least 4 to 1. In an attempt to keep pace with prior advancements in road bike technology, and to serve the new demand created by the popularity of mountain bikes, advanced equipment and materials are being developed within the bicycle industry to improve speed, safety and pedalling efficiency of mountain bikes. With the exception of lightweight composites and high-tech metals to decrease the overall weight of the bicycle, the single most significant improvement in bicycle accessories is the clipless pedal.
Clipless pedals have been available for road bikes, both for racing and touring, for many years. They provide increased comfort and decreased weight as compared with old style bicycle clips and pedals. Several disadvantages of prior clipless pedal systems were eliminated by the clipless pedal system disclosed in U.S. Pat. No. 4,942,778, issued Jul. 24, 1990 to the present inventor. One of the major disadvantages of earlier pedals was that the locking mechanism was in the pedal itself, limiting engagement of pedal and cleat to only one side of the pedal. As disclosed in the '778 patent, the locking mechanism is in the cleat which attaches to the sole of the shoe such that the mechanism is recessed and, thus, protected from damage.
Mountain biking introduces additional concerns beyond those for road bikes. The pedal bodies themselves are broader because they must bear a considerable amount of stress and strain when riding in rough terrain and during sudden changes of direction. Also, dirt and debris can build up on the pedals and in the cleats when riding off-road or in muddy conditions, so considerations must be made to avoid jamming the locking mechanism so that it will not engage or disengage when desired. Finally, because a rider may wish to leave his or her feet free when riding in rough terrain, it may be preferable to provide for a choice between locking the cleat and pedal together and riding "unattached". Thus, in a race situation, for example, the rider could be locked in when riding in areas where the course is predictable to achieve maximum pedalling efficiency, then release the pedals when he or she wants to be sure that a foot will be available to push off of an obstacle, to pivot in a sudden turn or to prevent a fall.
The clipless mountain bike pedals that are currently available, such as the Shimano SPD, the Time.TM. TMT and the LOOK.TM. "Moab" and "Nevada", among others, are bulky and complex, with spring mechanisms that require adjustment of the tension and which could become difficult to engage when caked with mud. Further, these pedals limit all but a very slight angular mobility of the foot (rotation of less than 10.degree.). This limitation is problematic because, while pedalling, mechanics are such that the rider's lower leg rotates. If the foot is fixed it forces the knee and its supporting tendons and ligaments to absorb this rotation, leading to chronic knee or ankle pain. In addition, mobility is especially needed in mountain bike riding where the rider frequently must shift his or her weight to negotiate rough terrain and sharp turns.